Capacitive-type position and reference angular rotation detecting apparatus

ABSTRACT

There is provided a capacity type rotation detecting apparatus which comprises a first insulating circular plate having on one surface thereof at least one pair of sets of electrode pieces arranged circumferentially and connected electrically to one another and at least one ring-shaped electrode, a second insulating circular plate having on one surface thereof at least one set of electrode pieces arranged circumferentially to face the at least one pair of sets of electrode pieces on the first insulating circular plate and connected electrically to one another and at least one ring-shaped electrode arranged to face the at least one ring-shaped electrode on the first plate and connected electrically to the at least one set of electrode pieces on the second plate, and a periodic signal supply circuit for applying periodic signals of opposite phase to the at least one pair of electrode-piece sets, respectively, on the first insulating circular plate, whereby, when the first and second insulating circular plates are placed facing each other and rotated relative to each other, the phase relation between the periodic signals transmitted to the at least one ring-shaped electrode on the first insulating circular plate through the capacitance formed between the opposite electrodes of the first and second plates and the periodic signals from the periodic signal supply circuit is detected and a rotational position signal and a reference angular position signal are generated simultaneously in accordance with the results of the phase detection.

This is a division of application Ser. No. 06/358,903, filed Mar. 17,1982 now U.S. Pat. No. 4,499,465.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for detecting therotational angular positions of the crankshaft of an engine in anautomobile or the like, particularly a rotation detecting apparatuscapable of detecting the reference angular position and incrementalrotational positions of a rotating object such as the crank shaft of anengine without any delay irrespective of its rotational speed. Moreparticularly, the invention relates to a capacity type rotationdetecting apparatus in which the transmission of signals is effected bymeans of the capacitance between the electrodes arranged opposite to oneanother.

2. Description of the Prior Art

The apparatuses heretofore known for detecting the rotation of thecrankshaft of an automobile engine include those in which a magneticmember having a coil would thereon is positioned opposite to arotational member and an alternating electromotive force is induced inthe coil in response to the magnetic flux variations caused by theprojections on the rotational member, thereby detecting the rotation ofthe rotational member.

However, this type of apparatus is disadvantaneous in that thealternating electromotive force induced in the coil is affected by themagnetic flux variations, that is, by the rotational speeds of therotational member and thus, if the rotational speed of the rotationalmember is low, practically no alternating electromotive force is inducedin the coil, making it impossible to detect the rotation of therotational member.

Another disadvantage is that where the detection of incrementalrotational angle signals (i.e., rotational position signals) andreference angular position signals is required, respective correspondingprojections must be separately arranged on the rotational member anddetecting means must be provided at two places making the constructioncomplicated.

SUMMARY OF THE INVENTION

With a view to overcoming the foregoing deficiencies in the prior art,it is an object of this invention to provide a capacity type rotationdetecting apparatus which is capable of accurately detecting theincremental rotational position and reference angular position of arotational member under measurement irrespective of its rotational speedand also capable of detecting the incremental rotational position andreference angular position within one and the same apparatus.

More specifically, this invention has the following objects.

(1) The first object of the invention is to provide a capacity typerotation detecting apparatus comprising a first plate and a second platearranged opposite to the first plate, the first plate having first andsecond electrodes of a first input part which are arranged along acircumference at respective equally given intervals and contiguouslyintermeshed and third and fourth electrodes of a second input partarranged along the same circumference, the second plate havingelectrodes of a first output part arranged along a circumference atrespective equally given intervals to face the first plate-firstinput-first and second electrodes and electrodes of a second output partwhich are arranged to face the first plate-second input-third and fourthelectrodes, whereby when one of the plates is rotated so that the firstelectrode of the first plate faces the first output electrodes of thesecond plate and the second electrode of the first plate faces the firstoutput electrodes of the second plate, respectively, these twoconditions are detected by detecting periodic signal voltages ofopposite phase, which are applied to the first and second electrodes ofthe first plate, by the first output electrodes of the second plate,thereby detecting the incremental rotational position of the rotationalmember satisfactorily, and also when the third electrode of the firstplate faces the second output electrode of the second plate and thefourth electrode of the first plate faces the second output electrode ofthe second plate, respectively, these two conditions are detected bydetecting periodic signal voltage of opposite phase, which are appliedto the third and fourth electrodes of the first plate, by the secondoutput electrodes of the second plate, thereby simultaneously andaccurately detecting the reference angular position of the rotationalmember under measurement irrespective of its rotational speed.

(2) The second object of the invention is to provide a capacity typerotation detecting apparatus comprising a first plate having electrodesof first and second input parts arranged at respective equally givenintervals and contiguously intermeshed along a first circumference,electrode pieces of a third input part which are arranged along a secondcircumference at respective different intervals therebetween, electrodepieces of a fourth input part which are arranged at respective equallygiven intervals with respect to the third input electrode pieces andfirst, second, third and fourth ring-shaped electrodes, a second platearranged opposite to the first plate and having first detectionelectrodes which are arranged to face the first plate-first and secondinput electrodes, second detection electrodes arranged so that all ofthe electrodes thereof face the first plate-third and fourth inputelectrodes once for every plate rotation and first, second, third andfourth ring-shaped electrodes respectively facing the first, second,third and fourth ring-shaped electrodes of the first plate andelectrically coupled to the first, second, third and fourth outputelectrodes, respectively, a periodic signal supply circuit for supplyingperiodic signals of opposite phases at a predetermined period to thefirst plate-first and second input electrodes and the first plate-thirdand fourth input electrodes, respectively, an incremental rotationalposition signal generating circuit for generating an incrementalrotational position signal of the second plate in response to thesignals appearing at the second plate-first and second output electrodeswhen the second plate is rotated relative to the first plate, and areference angular position signal generating circuit for generating areference angular position signal in response to the signals appearingat the second plate-third and fourth output electrodes.

(3) The third object of the invention is to provide a capacity typerotation detecting apparatus comprising a first plate having electrodepieces of first and second input parts arranged along a circumference atrespective equally given intervals and contiguously intermeshed, thefirst and second input electrode pieces providing a first inputreference angular position detection electrode comprising a set of thefirst input electrode pieces arranged at respective different intervalstherebetween, a second input reference angular position detectionelectrode comprising a set of the second input electrode pieces each ofwhich is adjacent to an associated one of the first input referenceangular position detection electrode pieces at one side thereof, a firstinput incremental rotational position detection electrode comprising aset of the first input electrode pieces other than the first inputreference angular position detection electrode pieces and a second inputincremental rotational position detection electrode comprising a set ofthe second input electrode pieces other than the second input referenceangular position detection electrode pieces and arranged contiguouslyintermeshed with the first input incremental rotational positiondetection electrode pieces and first and second ring-shaped electrodes,a second plate having electrodes of first and second output partsarranged respectively to face the reference angular position detectionelectrodes of the first and second input parts and first and secondring-shaped electrodes respectively connected to the first and secondoutput electrodes, and a detecting circuit for applying periodic signalsof opposite phases to the reference angular position detectionelectrodes of the first and second input parts at a predetermined periodand also applying periodic signals of opposite phases to the incrementalrotational position detection electrodes of the first and second inputparts at a period which is different from that of the periodic signalsapplied to the reference angular position detection electrodes of thefirst and second input parts, thereby detecting the incrementalrotational position and reference angular position of the second platein response to the periodic signals appearing at the first and secondoutput electrodes when the second plate is rotated relative to the firstplate.

(4) The fourth object of the invention is to provide a capacity typerotation detecting apparatus comprising a first plate having electrodepieces of first and second input parts which are arranged along acircumference at respective equally given intervals and contiguouslyintermeshed, the first and second input electrode pieces providing afirst input reference angular position detection electrode comprising aset of the first input electrode pieces arranged at respective differentintervals therebetween, a second input reference angular positiondetection electrode comprising a set of the second input electrodepieces each of which is adjacent to an associated one of the first inputreference angular position detection electrode pieces at one sidethereof, a first input incremental rotational position detectionelectrode comprising a set of the first input electrode pieces otherthan the first input reference angular position detection electrodepieces and a second input incremental rotational position detectionelectrode comprising a set of the second input electrode pieces otherthan the second input reference angular position detection electrodepieces and a ring-shaped electrode, a second plate having an outputelectrode which is arranged to face the reference angular positiondetection electrodes of the first and second input parts and aring-shaped electrode connected to the output electrodes, and adetecting circuit for applying periodic signals of opposite phases tothe first and second input reference angular position detectionelectrodes at a predetermined period and also applying periodic signalsof opposite phases to the first and second input incremental rotationalposition detection electrodes at a period which is different from thatof the periodic signals applied to the first and second input referenceangular position detection electrodes, thereby detecting the incrementalrotational position and reference angular position of the second platein response to the periodic signals appearing at the output electrodewhen the second plate is rotated relative to the first plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are respectively a partially cutaway view and alongitudinal sectional view showing a first embodiment of the rotationdetecting apparatus containing the first and second plates each thereofhaving the electrode structure according to this invention.

FIGS. 2a and 2b are front views showing respectively the electrodestructure of the first and second plates in the apparatus shown in FIG.1.

FIG. 3 is a circuit diagram showing an embodiment of the detectingcircuit section of the apparatus shown in FIG. 1.

FIGS. 4a and 4b are circuit diagrams showing respectively the relativepositions of the electrodes of the first input part and the first outputpart shown in FIGS. 2a and 2b, occurring during the rotation of therotational member, and useful for explaining the incremental rotationalposition signal detecting operation of the apparatus shown in FIG. 1.

FIG. 5 shows a plurality of signal waveforms which are useful forexplaining the incremental rotational position signal detectingoperation of the apparatus shown in FIG. 1.

FIGS. 6a and 6b are circuit diagrams showing respectively the relativepositions of the electrodes of the second input part and the secondoutput part shown in FIGS. 2a and 2b, occuring during the rotation ofthe rotational member, and useful for explaining the reference angularposition signal detecting operation of the apparatus shown in FIG. 1.

FIG. 7 shows a plurality of signal waveforms which are useful forexplaining the reference angular position detecting operation of theapparatus shown in FIG. 1.

FIG. 8 is a circuit diagram of a partial modification of the apparatusof the first embodiment of this invention.

FIGS. 9a and 9b are front views showing respectively the electrodestructure of the first and second plates of a capacity type rotationdetecting apparatus of a second embodiment of this invention.

FIGS. 10a and 10b are circuit diagrams showing the relative positions ofthe first and second input electrodes of the first plate and the firstdetection electrodes of the second plate shown in FIGS. 9a and 9b,occurring during the rotation of the rotational member, and useful forexplaining the operation of the apparatus of the second embodiment ofthis invention.

FIGS. 11a, 11b and 11c are circuit diagrams showing respectively therelative positions of the third and fourth input electrodes of the firstplate and the second detection electrodes of the second plate shown inFIGS. 9a and 9b, occurring during the rotation of the rotational member,and useful for explaining the operation of the apparatus of the secondembodiment of this invention.

FIG. 12 shows a plurality of signal waveforms which are useful forexplaining the reference angular position detecting operation of thesecond embodiment of this invention.

FIG. 13 is a longitudinal sectional view of a capacity type rotationdetecting apparatus of a third embodiment of this invention.

FIGS. 14a and 14b are front views showing respectively the first plateand the second plate used in the apparatus shown in FIG. 13.

FIG. 15 is a circuit diagram showing an embodiment of the detectingcircuit section of the apparatus shown in FIG. 13.

FIGS. 16a to 16f are circuit diagrams showing respectively the relativepositions of the electrodes occurring during the rotation of therotational member, which are useful for explaining the operation of theapparatus shown in FIG. 13.

FIG. 17 shows a plurality of signal waveforms which are useful forexplaining the operation of the detecting circuit section shown in FIG.15.

FIG. 18 is a longitudinal sectional view showing a capacity typerotation detecting apparatus of a fourth embodiment of this invention.

FIGS. 19a and 19b are front views showing the first and second platesused in the apparatus shown in FIG. 18.

FIG. 20 is a circuit diagram showing an embodiment of the detectingcircuit section of the apparatus shown in FIG. 18.

FIG. 21a to FIG. 21d show respectively the relative positions of theelectrodes occurring during the rotation of the rotational member, whichare useful for explaining the operation of the apparatus shown in FIG.18.

FIG. 22 shows a plurality of signal waveforms which are useful forexplaining the operation of the detecting circuit section of theembodiment shown in FIG. 20.

FIG. 23 shows a plurality of signal waveforms useful for explaining theoutput signals of the detecting circuit section shown in FIG. 20.

In the drawings, like reference numerals and symbols refer tocorresponding parts or items.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in greater detail withreference to its preferred embodiments illustrated in the accompanyingdrawings. The first embodiment shown in FIGS. 1a and 1b to FIG. 5 willbe described firstly.

Referring first to FIGS. 1a and 1b, numeral 100 designates a housingfixedly mounted on the outer side of a bearing 110, and 120 a shaftfixedly mounted on the inner side of the bearing 110 and coupled forexample to the crankshaft of an engine such that the rotation of theshaft 120 causes the rotation of a rotational member 160 fastened byscrews 190 to the shaft 120. Also fastened by screws 180 to therotational member 160 is a second plate 150 (rotating plate) comprisinga printed board having electrodes formed thereon by printing and adaptedto be rotated by the rotation of the rotational member 160. Also, afirst plate 140 (stationary plate) comprising a printed board havingelectrodes formed thereon by printing is fastened by screws 170 to thehousing 100 and connected to the first plate 140 are signal lines 141-a,142-a, 143-a, 144-a, 145-a, 146-a, 147-a and 148-a from a detectingcircuit section 101 provided on a printed board 130 which is fastened tothe housing 100.

FIG. 2a shows a surface 140a of the first plate 140 which faces thesecond plate 150, and the signal lines 141-a, 142-a, 143-a, 144-a,145-a, 146-a, 147-a and 148-a are respectively connected via connectingpoints 21, 22, 23, 24, 25, 26, 27 and 28 to a first electrode 141 and asecond electrode 142 of a first input part, a first ring-shapedelectrode 143, a second ring-shaped electrode 144, a third ring-shapedelectrode 145, a fourth ring-shaped electrode 146, and third and fourthsemi-circular electrodes 147 and 148 of a second input part arranged onthe same circumference, which are formed on the first plate 140. Thefirst and second electrodes 141 and 142 of the first input part (i.e.,first and second first-input electrodes) are arranged circumferentiallyat respectively equally given intervals and contiguously intermeshed.

FIG. 2b shows a surface 150a of the second plate 150 which faces thefirst plate 140 and its pectinated first electrode 151 of a first outputpart is connected by a lead wire 151a to a first ring-shaped electrode153 and second electrode 152 of the first output part is connected by alead wire 152a to a second ring-shaped electrode 154. The first andsecond electrodes 151 and 152 (constituting first-output electrodemeans) are arranged circumferentially at respective equally givenintervals and contiguously intermeshed.

On the other hand, a third semi-circular electrode 157 of a secondoutput part is connected by a lead wire 157a to a third ring-shapedelectrode 155 and a fourth semi-circular electrode 158 of the secondoutput part is connected by a lead wire 158a to a fourth ring-shapedelectrode 156. The third and fourth electrodes 157 and 158 of the secondoutput part (constituting a second-output electrode means) are arrangedalong the same circumference. The plates 140 and 150 have theirelectrodes printed such that the electrodes 141 and 151, the electrodes142 and 152, the electrodes 143 and 153, the electrodes 144 and 154, theelectrodes 145 and 155, the electrodes 146 and 156, the electrodes 147and 157 and the electrodes 148 and 158 are respectively positioned toface each other and pass over each other during rotation.

FIG. 3 shows a circuit diagram of the detecting circuit section 101. Inthe Figure, a terminal 301 is a power supply terminal to which isapplied a fixed voltage +V_(C). A terminal 302 is a ground terminal.Numeral 310 designates a known type CR oscillator circuit, and 320designates a reference signal generating circuit. The circuits 310 and320 form a periodic signal supply circuit. Numeral 330 designates acapacitor group comprising the upper electrodes 151, 152, 153 and 154and the lower electrodes 141, 142, 143 and 144. Numeral 340 designates afirst comparison circuit, and 350 a first phase detecting circuit. Thecircuits 340 and 350 form an incremental rotational position signalgenerating circuit. Numeral 303 designates a first output terminal(incremental rotational position signal output terminal).

Numeral 360 designates a reference angular position signal detectorincluding a capacitor group comprising the upper electrodes 155, 156,157 and 158 and the lower electrodes 145, 146, 147 and 148. Numeral 370designates a second comparison circuit, and 380 a second phase detectingcircuit. The circuits 370 and 380 form a reference angular positionsignal generating circuit. Numeral 304 designates a second outputterminal (reference angular position signal output terminal).

With the construction described above, the operation of the firstembodiment will now be described. In FIG. 3, the oscillation waveform 10shown in (a) of FIG. 5 is produced by an oscillator circuit comprisinginverter gates 311, 312 and 313, resistors 314 and 315 and a capacitor316 of the CR oscillator circuit 310. This oscillation waveform 10 isthen transmitted to the reference signal generating circuit 320 so thata signal of the same phase as the oscillation waveform 10 and the signalof the opposite phase shown in (b) of FIG. 5 are generated. The methodof incremental rotational position signal detection will be describedfirst. Description will be made with reference to a case where the shaft120 (shown in FIG. 1) is rotated so that the first electrode 151 of thefirst output means is positioned opposite to the first-input firstelectrode 141 of the first plate 140, and the first-output secondelectrode 152 of the second plate 150 is positioned opposite thefirst-input second electrode 142 of the first plate 140 as shown in FIG.4a. When the signal of the same phase as the oscillation waveform 10 isapplied to the first-input first electrode 141 of the first plate 140, asignal of the same phase as the oscillation waveform 10 is generated onthe signal line 151a shown in FIG. 2b by a capacitor (331 in FIG. 3),comprised of the first-input first electrode 141 of the first plate 140and the first output-first electrode 151 of the second plate 150, andthis signal is transmitted as the signal 30 shown in (C) of FIG. 5 tothe first comparison circuit 340 via the connecting point 23 by acapacitor (332 in FIG. 3), comprised of the first ring-shaped electrode153 of the second plate 150 and the first ring-shaped electrode 143 ofthe first plate 140. In like manner, the signal 20 transmitted to thefirst-input first-second electrode 142 of the first plate 140 via thesignal line 142-a appears as a signal of the same phase as signal 20 atthe first-output second electrode 152 of the second plate 150 by acapacitor (333 in FIG. 3), comprised of the first-input second electrode142 and the first-output second electrode 152, and then the signal istransmitted as the signal 40 shown in (d) of FIG. 5 to the firstcomparison circuit 340 via the connecting point 24 by a capacitor (334in FIG. 3), comprised of the second ring-shaped electrode 154 of thesecond plate 150 and the second ring-shaped electrode 144 of the firstplate 140. It is to be noted that each of the signals 30 and 40 has awaveform using as a bias voltage the voltage Va shown in (c) and (d) ofFIG. 5 and determined by voltage dividing resistors 343 and 344 of thefirst comparison circuit 340. Then, the signals 30 and 40 aredifferentially amplified by a differential amplifier comprising anoperational amplifier 346 (hereinafter referred to as an OP AMP) and aresistor 345 and thus an output signal 50 is produced which is delayedfrom the oscillation waveform 10 by a time ΔT and having the waveformshown in (e) of FIG. 5. Note that the time ΔT-represents the capacitorresponse delay time and the switching delay time of the OP AMP 346.

Then, the waveform of the signal 50 is reshaped by inverter gates 347and 348 so that a waveform of the same phase as the signal 50 is appliedto the data terminal of D-type flip-flops 351 and 352, respectively.Also, a signal of the same phase as the oscillation waveform 10 isapplied from the oscillator circuit 310 to the clock terminal of theD-type flip-flop 352 and a signal of the phase opposite to theoscillation waveform 10 is applied to the clock terminal of the D-typeflip-flop 351. Thus, the output terminal Q of the D-type flip-flop 351goes to "0" and the output terminal Q of the D-type flip-flop 352 goesto "1". Then, an output signal 60 whose level is shown by the "0" signalin (f) of FIG. 5 appears through NAND gates 353, 354, 355 and 356. Thissignal is transmitted to an output circuit comprising a transistor 358and resistors 357 and 359 so that the transistor 358 is turned offthrough the resistor 357 and an incremental rotational position signal"1" (the signal 70 shown in (g) of FIG. 5) is generated at the firstoutput terminal 303 indicating that the first-output first electrode 151of the second plate 150 is opposite the first-input first electrode 141of the first plate 140 (or the first-output second electrode 152 of thesecond plate 150 is opposite the first-input second electrode 142 of thefirst plate 140).

On the other hand, when the first-output first electrode 151 of thesecond plate 150 is opposite the first-input second electrode 142 of thefirst plate 140, and the first-output second electrode 152 of the secondplate 150 is opposite the first-input first electrode 141 of the firstplate 140 as shown in FIG. 4b, a signal of the same phase as the signal20 is generated at the first-output first electrode 151 of the secondplate 150 so that, as mentioned previously, the signal 31 shown in (c)of FIG. 5 and using Va as the bias voltage is generated at the firstring-shaped electrode 143 of the first plate 140, and also a signal ofthe same phase as the oscillation waveform 10 is generated at thefirst-output second electrode 152 of the second plate 150 so that thesignal 41 shown in (d) in FIG. 5 and using Va as the bias voltage isgenerated at the second ring-shaped electrode 144 of the first plate140. Then, a signal such as shown by the signal 51 in (e) of FIG. 5 isgenerated at the output terminal of the first comparison circuit 340 sothat the signal 61 in (f) of FIG. 5 is generated at the output terminalof the NAND gates 355 and 356 of the first phase detecting circuit 350and an incremental rotational position signal "0" (the signal 71 shownin (g) of FIG. 5) is generated at the first output terminal 303indicating that the first-output first electrode 151 of the second plate151 is opposite the first-input second electrode 142 of the first plate140.

In this way, the first-output first and second electrodes 151 and 152arranged on the second plate 150 pass over the first-input first andsecond electrodes 141 and 142 arranged on the first plate 140 inresponse to the rotation of the shaft 120, and "1" and "0" signals arealternately generated at the first output terminal 303, therebydetecting the incremental rotation of the second plate 150 or theincremental rotation of the shaft 120.

Next, the method of the reference angular position signal detection willbe described.

Description will be made first with reference to a case where thesecond-output third electrode 157 of the second plate 150 is oppositethe second-input third electrode 147 of the first plate 140 and thesecond-output fourth electrode 158 of the second plate 150 is oppositethe second-input fourth electrode 148 of the first plate 140 as shown inFIG. 6a. The previously mentioned signals 10 and 20 generated from thereference signal generating circuit 320 are respectively applied to thesecond-input third and fourth electrodes 147 and 148 of the first plate140. Thus, a signal of the same phase as the signal 10 appears at thesecond output third electrode 157 of the second plate 150 and thissignal is transmitted by a capacitor (the capacitor 362 in FIG. 3),comprised of the third ring-shaped electrode 155 of the second plate 150and the third ring-shaped electrode 145 of the first plate 140, therebygenerating at the third ring-shaped electrode 145 of the first plate 140the signal 81 shown in (c) of FIG. 7 and using Va as the bias voltage.In like manner, a signal of the same phase as signal 20 appears at thesecond-output fourth electrode 158 of the second plate 150 and thissignal is transmitted through a capacitor (the capacitor 364 in FIG. 3),comprised of the fourth ring-shaped electrode 156 of the second plate150 and the fourth ring-shaped electrode 146 of the first plate 140,thereby generating at the fourth ring-shaped electrode 146 of the firstplate 140 the signal 82 shown in (d) of FIG. 7 and using Va as the biasvoltage. These signals are transmitted to the second comparison circuit370 which in turn produces at its output terminal the signal shown by 83in (e) of FIG. 7, so that the signal 84 in (f) of FIG. 7 is generated atthe output terminal of the second phase detecting circuit 380 and asignal "1" (the signal 85 in (g) of FIG. 7) is generated at the secondoutput terminal 304 indicating that the second-output third electrode157 of the second plate 150 is opposite the second-input third electrode147 of the first plate 140.

Then, when the second-output third electrode 157 of the second plate 150is positioned opposite the second-input fourth electrode 148 of thefirst plate 140 and the second-output fourth electrode 158 of the secondplate 150 is positioned opposite the second-input third electrode 147 ofthe first plate 140 as shown in FIG. 6b, a signal of the same phase asthe signal 20 (the signal 86 in (c) of FIG. 7) appears at the thirdring-shaped electrode 145 of the fist plate 140 and a signal of the samephase as the signal 10 (the signal 87 in (d) of FIG. 7) appears at thefourth ring-shaped electrode 146 of the first plate 140. As a result,the signal shown by 88 in (e) of FIG. 7 is generated at the outputterminal of the second comparison circuit 370 and the signal 89 in (f)of FIG. 7 is generated at the output terminal of the second phasedetecting circuit 380, thereby generating at the second output terminal304 a signal "0" (the signal 90 in (g) of FIG. 7) indicating that thethird semi-circular electrode 157 of the second plate 150 is oppositethe fourth semi-circular electrode 148 of the first plate 140.

In this manner, the signal appearing at the second output terminal 304goes from the "1" level to the "0" level once for every rotation of theshaft 120 and thus, by using the leading edge or the falling edge ofthis signal as a reference angular position signal, it is possible toobtain an accurate reference angular position.

While, in the first embodiment described above, the first and secondelectrodes 151 and 152 and the third and fourth electrodes 157 and 158are provided respectively as the electrodes of the first and secondinputs of the second plate 150, and the signals appearing at theseelectrodes are compared by the first and second comparison circuits 340and 370, respectively, one or the other of the electrodes of the firstand second inputs, respectively, may be eliminated. For instance, whereonly the first electrode 151 is used as the first output electrodes andthe third electrode 157 as the second output electrode, only the firstand third electrodes 153 and 155 are required as the ring-shapedelectrodes. The circuit diagram of FIG. 8 shows a modified form of therotational position signal detector 330, the reference angular positionsignal detector 360 and the first and second comparison circuits 340 and370 for this purpose. In this case, the same results as theabove-described first embodiment can be obtained by comparing thesignals appearing at the first and third ring-shaped electrodes 153 and155 with the predetermined voltage Va in the first and second comparisoncircuits 340 and 380, respectively, to generate an output.

Next, the second embodiment of the invention will be described. Itsconstruction will be described first with reference to FIGS. 9a and 9b.

FIG. 9a is a front view showing a surface 140a of a first (fixed) plate140 which faces a second (rotatable) plate 150. In the construction ofthe first embodiment shown in FIG. 1b which is used in common with thefirst and second embodiments, signal lines 141-a, 142-a, 143-a, 144-a,145-a, 146-a, 147-a and 148-a are respectively connected via connectingpoints 21A, 22A, 23A, 24A, 25A, 26A, 27A and 28A to first, second, thirdand fourth input electrodes 141, 142, 143 and 144 each having aplurality of pectinated electrode pieces and first, second, third andfourth ring-shaped electrodes 145A, 146A, 147A and 148A of a first plate140. Here, the first and second input electrodes 141 and 142 of thefirst plate 140 are arranged along a first circumference at respectiveequally given intervals and contiguously intermeshed, and the thirdinput electrode 143A is arranged along a second circumference with allthe adjacent electrode pieces arranged at respective differentintervals. The fourth input electrode 144A of the first plate 140 isarranged along the second circumference at respective equally givenintervals with respect to the third input electrode 143A in the samedirection along the second circumference.

FIG. 9b is a front view showing a surface 150a of a second plate 150which faces the first plate 140, and first and second output electrodes151 and 152 which form first detection electrodes of the second plate150 are arranged to face the first and second input electrodes of thefirst plate 140. Also, third and fourth output electrodes 153A and 154Awhich form second detection electrodes of the second plate 150 arearranged such that all the electrodes are positioned opposite to thethird and fourth input electrodes 143A and 144A of the first plate 140only once for every rotation of the second plate 150 with respect to thefirst plate 140. Also, first, second, third and fourth ring-shapedelectrodes 155A, 156A, 157A and 158A of the second plate 150 arearranged at positions respectively opposing the first, second, third andfourth ring-shaped electrodes 145A, 146A, 147A and 148A of the firstplate 140, and the first, second, third and fourth ring-shapedelectrodes 155A, 156A, 157A and 158A of the second plate 150 arerespectively connected to the first, second, third and fourth outputelectrodes 151, 152, 153A and 154A of the second plate 150.

Next, the construction of the detecting circuit section 101 in FIG. 1bis substantially the same with the construction shown in FIG. 3 for thefirst embodiment. The only differences reside in that the capacitorgroup forming the rotational position signal detector 330 comprises theelectrodes 151, 152, 155A and 156A of the second plate 150 and theelectrodes 141, 142, 145A and 146A of the first plate 140 and that thecapacitor group forming the reference angular position signal detector360 comprises the electrodes 153A, 154A, 157A and 158A of the secondplate 150 and the electrodes 143A, 144A, 147A and 148A of the firstplate 140. As regards the method of rotational position signal detectionwhich is one of the functions of the detecting circuit section 101,FIGS. 10a and 10b for explaining the method correspond to FIGS. 4a and4b for the first embodiment and also the corresponding signal waveformdiagram is all the same with FIG. 5 for the first embodiment. Thus, thefunction is identical with that of the first embodiment and itsexplanation is omitted. Only the method of reference angular positionsignal detection which is different from that of the first embodimentwill be described with reference to FIGS. 11a, 11b, 11c and 12. Notethat those signals generated in respose to the relative positions of theopposing electrodes of the first and second plates 140 and 150correspond respectively to the waveform diagrams shown in the left,center and right portions of (c) to (g) of FIG. 12.

Description will be made first with reference to a case where the wholeof the fourth output electrode 154A of the second plate 150 ispositioned opposite to the whole of the third input electrode 143A ofthe first plate 140 as shown in FIG. 11a. In this case, all theelectrode pieces of the third output electrode 153A of the second plate150 are facing none of the input electrodes of the first plate 140. Thesignals 10 and 20 generated from the reference signal generating circuit320 are respectively applied to the third and fourth input electrodes143A and 144A of the first plate 140 so that a signal of the same phaseas the signal 10 is generated at the fourth output electrode 154A of thesecond plate 150 and this signal is transmitted to the second comparisoncircuit 370 by way of a capacitor (the capacitor 364 in FIG. 3)comprising the fourth ring-shaped electrode 158A of the second plate 150and the fourth ring-shaped electrode 148A of the first plate 140,thereby generating at the fourth ring-shaped electrode 148A of the firstplate 140 the signal 82 shown in (d) in FIG. 12 and biased by thevoltage Va. Since the third output electrode 153A of the second plate150 is not facing any of the input electrodes of the first plate 140 asmentioned previously, no signal is generated at the third-ring shapedelectrode 147A of the first plate 140. The signal 82 is amplified by thesecond comparison circuit 370 so that it is generated as a signal 83whose waveform is reshaped by the inverter gates 373 and 374 and asignal of the same phase as the signal 83 is transmitted to the secondphase detecting circuit 380. As a result, the signal 84 shown in (f) ofFIG. 12 is generated on the output line 84 of the second phase detectingcircuit 380 (see FIG. 3) and the signal appears as a "1" level signalsuch as shown by the signal 85 in (g) of FIG. 12 at the referenceangular position signal output terminal 304.

Next, when the third output electrode 153A of the second plate 150 ispositioned opposite to the third input electrode 143A of the first plate140 shown in FIG. 11a and the fourth output electrode 154A of the secondplate 150 is opposite to the fourth input electrode 144A of the firstplate 140 as shown in FIG. 11b, a signal of the same phase as theoscillation waveform 10 (the signal 86 in FIG. 10) is generated at thethird ring-shaped electrode 147A of the first plate 140 and a signal ofthe same phase as the signal 20 (the signal 87 in FIG. 12) appears atthe fourth ring-shaped electrode 148A of the first plate 140 so that thesignal shown by 88 in (e) of FIG. 12 is generated at the output terminalof the second comparison circuit 370 and the signal 89 in (f) of FIG. 12is generated at the output terminal of the second phase detectingcircuit 380. Thus, a signal "0" (the signal 90 in FIG. 12) is generatedat the reference angular position signal output terminal 304 indicatingthat the third output electrode 153A of the second plate 150 is oppositeto the third input electrode 143A of the first plate 140.

Then, when the third output electrode 153A of the second plate 150 ispositioned opposite to the fourth input electrode 144A of the firstplate 140 shown in FIG. 11a as shown in FIG. 11c, a signal 91 (see (c)of FIG. 12) of the same phase as the signal 20 is generated at the thirdring-shaped electrode 147A of the first plate 140. At this time, thefourth output electrode 154A of the second plate 150 is not facing theinput electrodes of the first plate 140 and thus no signal is generatedat the fourth ring-shaped electrode 148A of the first plate 140. Then,the signal 91 is amplified by the second comparison circuit 370 so thatthe signal 92 shown in (e) of FIG. 12 is generated at the outputterminal of the second comparison circuit 370 and the signal 93 in (f)of FIG. 12 is generated at the output terminal of the second phasedetecting circuit 380, thereby generating a "1" signal (the signal 94 in(g) of FIG. 12) at the reference angular position signal output terminal304.

On the other hand, when the shaft 120 is rotated so that the secondplate 150 is rotated, at any other position than those described inconnection with FIGS. 11a, 11b and 11c the third or fourth outputelectrode of the second plate 150 faces only one of the electrode piecesof the third or fourth electrode of the first plate 140 at the most, andthus this can be ignored.

In this way, the signal appearing at the second output terminal 304 goesfrom the "1" level to the "0" level or from the "0" level to the "1"level once for every rotation of the shaft 120 and thus, by using theleading edge or the falling edge of this signal as a reference angularposition signal, it is possible to obtain an accurate reference angularposition.

While, in the second embodiment described above, the first and secondoutput electrodes 151 and 152 and the third and fourth output electrodes153A and 154A are provided as the first detection electrodes and thesecond detection electrodes, respectively, of the second plate 150 andthe signals generated at these electrodes are respectively compared inthe first and second comparison circuits 340 and 370, one or the otherof the first and second detection electrodes, respectively, may beeliminated. For example, if only the first output electrode 151 is usedas the first detection electrode and only the third output electrode153A is used as the second detection electrode, only the first and thirdelectrodes 155A and 157A of the ring-shaped electrodes are required. Inthis case, as in the case of the electric circuitry of FIG. 8 for thefirst embodiment, the same result as the above-mentioned secondembodiment can be obtained by comparing the signals appearing at thefirst and third ring-shaped electrodes 155A and 157A with thepredetermined voltage Va in the first and second comparison circuits 340and 370, respectively, to generate an output.

The third embodiment of the invention will now be described withreference to FIGS. 13 to 17.

FIG. 13 is a longitudinal sectional view showing the mechanicalconstruction of a capacity type rotation detection apparatus accordingto the third embodiment of the invention similar to the case of FIG. 1bfor the first embodiment. In the third embodiment-however, the signallines 141-a, 142-a, 143-a, 144-a, 145-a and 146-a from the detectingcircuit section 101 provided on the printed board 130 attached to thehousing 100 are connected to the electrodes of the first plate 140. Inother words, in FIG. 14a illustrating a front view showing the surface140a of the first plate 140 which faces the second plate 150, its signallines 141-a, 142-a, 143-a, 144-a, 145-a and 146-a are connected viaconnecting points 40, 50, 60, 70, 25 and 26 to first and second inputreference angular position detection electrodes 141 and 142 and firstand second input rotational position detection electrodes 143 and 144,each including a plurality of pectinated electrode pieces, and first andsecond ring-shaped electrodes 145 and 146 of the first plate 140. Thefirst and second input reference angular position detection electrodes141 and 142 have their respective electrode pieces arranged atrespective different intervals and they are respectively interconnectedon the back surface via the connecting points 40 and 50. The first andsecond input rotational position detection electrodes 143 and 144 arearranged in a manner that their electrode pieces are radially arrangedalternately in those portions where the first and second input referenceangular position detection electrodes are not present and arerespectively interconnected on the front surface as well as on the backsurface via the connecting points 60 and 70, respectively. FIG. 14b is afront view showing the surface 150a of the second plate 150 which facesthe first plate 140, and first and second output electrodes 151 and 152are respectively connected electrically to ring-shaped electrodes 153and 154 by lead wires 155 and 156. Also it is so arranged that when thesecond plate 150 is rotated, the whole of the first and second outputelectrodes 151 and 152 are respectively positioned opposite to the firstand second input reference angular position detecting electrodes 141 and142 of the first plate 140 at only one position. The first and secondring-shaped electrodes 153 and 154 of the second plate 150 are arrangedat positions opposite to the first and second ring-shaped electrodes 145and 146 of the first plate 140.

FIG. 15 shows a circuit diagram of the detecting circuit section 101. Inthe Figure, a terminal 301 is a power supply terminal to which isapplied a constant voltage +V_(C). A terminal 302 is a ground terminal.Numeral 310 designates a known type CR oscillator circuit, 320 a firstreference signal generating circuit, 330 a second reference signalgenerating circuit, 340 a capacitor group comprising the electrodes 151,152, 153 and 154 of the second plate 150 and the electrodes 141, 142,143, 144, 145 and 146 of the first platel 140, 350 a comparison circuit,360 a phase detecting circuit, 370 a reference angular position signaloutput circuit, 380 a rotational position signal output circuit, 303 areference angular position signal output terminal, and 340 a rotationalposition signal output terminal.

The CR oscillator circuit 310 and the first reference signal generatingcircuit 320 form a first periodic signal supply circuit, and the CRoscillator circuit 310 and the second reference signal generatingcircuit 330 form a second periodic signal supply circuit. Also, thecomparison circuit 350, the phase detecting circuit 360, the referenceangular position signal output circuit 370 and the rotational positionsignal output circuit 380 form a detecting circuit.

With the construction described above, the operation of the circuitrywill now be described with reference to FIG. 15, FIGS. 16a to 16f andFIG. 17. In FIG. 15, the CR oscillator circuit 310 comprising invertergates 311 and 312, resistors 313 and 314 and a capacitor 315 producesthe oscillation waveform 10-s shown in (a) of FIG. 17. The oscillationwaveform 10-s is transmitted to the first reference signal generatingcorcuit 320, and the waveform 11-s shown in (c) of FIG. 17 obtained bythe 2:1 frequency division of the oscillation waveform 10-s and thewaveform 21-s shown in (d) of FIG. 17, which is opposite in phase to thewaveform 11-s, are produced through a D-type flip-flop 321 and invertergates 322, 323 and 324. The oscillation waveform 10-s is alsotransmitted to the second reference signal generating circuit 330, and asignal of the same phase as the oscillation waveform 10-s and the signal20-s of the opposite phase shown in (b) of FIG. 17 are generated there.

The operation will now be described with reference to a case where theshaft 120 of FIG. 13 is rotated so that the second plate 150 is alsorotated bringing its first output electrode 151 opposite to the firstinput rotational position detection electrode 143 of the first plate 140and the second output electrode 152 opposite to the second inputrotational position detection electrode 144 of the first plate 140 asshown in FIG. 16a. While this represents the case in which the first andsecond output electrodes 151 and 152 of the second plate 150,respectively, have, at the most, one of their electrode piecespositioned opposite to the first and second input electrodes 141 and 142of the first plate 140, this number is negligible as compared with thenumber of the first and second output electrode pieces facing the firstand second input rotational position detection electrodes 143 and 144,respectively, of the first plate 140 in this condition (the number ofthe electrode pieces is 4 at the least in this embodiment). A signal ofthe same phase as the oscillation waveform 10-s is generated on the leadwire 155 shown in FIG. 14b via the signal line 143-a and a capacitor(343 in FIG. 15) comprising the first input rotational positiondetection electrode 143 of the first plate 140 and the first outputelectrode 151 of the second plate 150 and the signal is then transmittedas a signal 30-s (see (e) of FIG. 17) to the comparison circuit 350 ofFIG. 15 via the connecting point 25 by a capacitor (345 in FIG. 15)comprising the first ring-shaped electrode 153 of the second plate 150and the first ring-shaped electrode 145 of the first plate 140. Also, asignal 20-s of the opposite phase to the oscillation waveform 10-s isapplied to the second input rotational position detection electrode 144of the first plate 140 via the signal line 144a so that a signal of thesame phase as the signal 20-s is generated on the lead wire 156 shown inFIG. 14b by way of a capacitor (344 in FIG. 15) comprising the electrode144 and the second output electrode 152 of the second plate 150 and thesignal is then transmitted as a signal 31-s (see (e) of FIG. 17) to thecomparison circuit 350 of FIG. 15 via the connecting point 26 by acapacitor (346 in FIG. 15) comprising the second ring-shaped electrode154 of the second plate 150 and the second ring-shaped electrode 146 ofthe first plate 140. Note that the waveforms of the signals 30-s and31-s are biased by the voltage Va determined by resistors 352 and 353 ofthe comparison circuit 350. The signals 30-s and 31-s are thendifferentially amplified by a differential amplifier circuit comprisingan operational amplifier 356 (hereinafter simply referred to as an OPAMP) and a resistor 355 of the comparison circuit 350 and the amplifiedsignal is then reshaped through inverter gates 357 and 358, therebygenerating a signal 50-s of the wveform shown in (l) of FIG. 17 anddelayed by ΔT with respect to the signal 20-s. Note that the delay ΔTrepresents the capacitor response delay time and the switching delaytime of the OP AMP 356.

The signal 50-s is transmitted to the phase detecting circuit 360 andapplied to the data input of its D-type flip-flops 363, 364, 365 and366, respectively. Also, the signal 60-s shown in (r) of FIG. 17 isapplied to the clock terminal of the D-type flip-flop 363 and a signalof the phase opposite to the signal 60-s is applied to the clockterminal of the D-type flip-flop 364. Also, the signal 70-s shown in (s)of FIG. 17 is applied to the clock terminal of the D-type flip-flop 365and a signal of the phase opposite to the signal 70-s is applied to theclock terminal of the D-type flip-flop 366. When the above-mentionedsignal 50-s is applied to the D-type flip-flops 363, 364, 365 and 366,respectively, a "0" is generated at the output terminal Q of the D-typeflip-flops 363 and 365, respectively, and a "1" is generated at theoutput terminal Q of the D-type flip-flops 364 and 366, respectively.The output signals of the D-type flip-flops 363, 364, 365 and 366 arethen transmitted to the rotational position signal output circuit 380 sothat a "0" is generated at the output terminal of a NAND gate 381 andalso a "0" is generated at the output terminal of a NAND gate 382. Thus,the input signal to a switching circuit comprising resistors 385 and 387and a transistor 386 goes to the low level and a signal "1" is generatedat the output terminal 304 indicating that the first output electrode151 of the second plate 150 is opposite to the first input rotationalposition detection electrode 143 of the first plate 140 (or the secondoutput electrode 152 of the second plate 150 is opposite to the secondinput rotational position detection electrode 144 of the first plate140). At this time, the signal at the output terminal 303 of thereference angular position signal output circuit 370 is "0". On theother hand, when the rotation of the shaft 120 of FIG. 13 rotates thesecond plate 150 so that its second output electrode 152 is positionedopposite to the first input reference angular position detectionelectrode 141 of the first plate 140 and its first output electrode 151is positioned opposite to the second input rotational angle detectionelectrode 144 of the first plate 140 as shown in FIG. 16b, the signal20-s applied to the second input rotational position detection electrode144 of the first plate 140 is transmitted as a signal 32-s (see (f) ofFIG. 17) to the comparison circuit 350 by way of a capacitor comprisingthe first output electrode 151 of the second plate 150 and the secondinput rotational position detection electrode 144 of the first plate 140and the capacitor comprising the first ring-shaped electrodes 145 and153 of the first and second plates 140 and 150. Also, the signal 11-sapplied to the first input reference angular position detectionelectrode 141 of the first plate 140 is applied as a signal 33-s (see(f) of FIG. 17) to the comparison circuit 350 by way of a capacitorcomprising the second output electrode 152 of the second plate 150 andthe first input reference angular position detection electrode 141 ofthe first plate 140 and the capacitor comprising the second ring-shapedelectrodes 146 and 164 of the first and second plates 140 and 150. Thesesignals are differentially amplified by the comparison circuit 350,reshaped through the inverters 357 and 358 and then transmitted as asignal 51-s (see (m) of FIG. 17) to the phase detecting circuit 360. Thephase detecting circuit 360 detects the phases of the signal 51-s andthe previously mentioned signals 60-s and 70-s so that a "0" isgenerated at the output terminal 304 of the rotational position signaloutput circuit 380. At this time, the signal at the output terminal 303of the reference angular position signal output circuit 370 remains "0".

When the shaft 120 is rotated further so that the first and secondoutput electrodes 151 and 152 of the second plate 150 are respectivelypositioned opposite to the first and second input reference angularposition detection electrodes 141 and 142 of the first plate 140 asshown in FIG. 16c, a signal 34-s (see (g) of FIG. 17) of the same phaseas the waveform 11-s applied to the first input reference angularposition detection electrode 141 of the first plate 140 is transmittedto the comparison circuit 350 by way of a capacitor comprising the firstinput reference angular position detection electrode 141 of the firstplate 140 and the first output electrode 151 of the second plate 150 andthe capacitor comprising the first ring-shaped electrodes 145 and 153 ofthe first and second plates 140 and 150. Also, a signal 35-s (see (g) ofFIG. 17) of the same phase as the waveform 21-s applied to the secondreference angular position detection electrode 142 of the first plate140 is transmitted to the comparison circuit 350 by way of a capacitorcomprising the second input reference angular position detectionelectrode 142 of the first plate 140 and the second output electrode 152of the second plate 150 and the capacitor comprising the secondring-shaped electrodes 146 and 154 of the first and second plates 140and 150. The signals 34-s and 35-s are differentially amplified andtransmitted as a signal 52-s (see (n) of FIG. 17) to the phase detectingcircuit 360. When the signal 52-s is transmitted to the phase detectingcircuit 360, the output terminals Q's of the D-type flip-flops 365 and366 go to "1" and the output terminals Q's of the D-type flip-flops 363and 364 go to "0". As a result, the output terminal of a NAND gate 374goes to "0" and the output terminal 303 of the reference angularposition output circuit 370 goes to "1". In this case, the rotationalposition signal output terminal 304 remains " 0".

Then, when the second input reference angular position detectionelectrode 142 of the first plate 140 and the first output electrode 151of the second plate 150 are positioned opposite to each other and alsothe first input rotational position detection electrode 143 of the firstplate 140 and the second output electrode 152 of the second plate 150are positioned opposite to each other as shown in FIG. 16d, the signal21-s is transmitted as a signal 36-s as shown in (h) of FIG. 17 to thecomparison circuit 350 by way of a capacitor comprising the second inputreference angular position detection electrode 142 of the first plate140 and the first output electroee 151 of the second plate 150 and thecapacitor comprising the first ring-shaped electrodes 145 and 153 of thefirst and second plates 140 and 150. Also, the signal 10-s istransmitted as the signal 37-s shown in (h) of FIG. 17 to the comparisoncircuit 350 by way of a capacitor comprising the first input electrode143 of the first plate 140 and the second output electrode 152 of thesecond plate 150 and the capacitor comprising the second ring-shapedelectrodes 146 and 154 of the first and second plates 140 and 150. Thesignals 36-s and 37-s are differentially amplified by the comparisoncircuit 350 so that the signal 53-s shown in (o) of FIG. 17 istransmitted to the phase detecting circuit 360 and the output terminal303 of the reference angular position signal output circuit 370 goes to"0". In this case, the output terminal 304 of the rotational positionsignal output circuit 380 remains "0".

When the shaft 120 is rotated further so that the first input rotationalposition detection electrode 143 of the first plate 140 and the firstoutput electrode 151 of the second plate 150 are opposite to each otherand also the second input rotational position detection electrode 144 ofthe first plate 140 and the second output electrode 152 of the secondplate 150 are opposite to each other as shown in FIG. 16e, signals 38-sand 39-s are transmittted to the comparison circuit 350 as shown in FIG.16e. Thus, the output terminal 304 of the rotational position signaloutput circuit 380 goes to the "1" level and the output terminal 303 ofthe reference angular position signal output circuit 370 remains at the"0" level.

When the shaft 120 is rotated further so that the second input electrode144 of the first plate 140 and the first output electrode 151 of thesecond plate 150 face each other and also the first input electrode 143of the first plate 140 and the second output electrode 152 of the secondplate 150 face each other as shown in FIG. 16f, the signal 20-s istransmitted as the signal 40-s shown in (j) of FIG. 17 to the comparisoncircuit 350 by way of a capacitor comprising the second input electrode144 of the first plate 140 and the first output electrode 151 of thesecond plate 150 and the capacitor comprising the first ring-shapedelectrodes 145 and 153 of the first and second plates 140 and 150. Also,a signal of the same phase as the oscillation waveform 10-s istransmitted as the signal 41-s shown in (j) of FIG. 17 to the comparisoncircuit 350 by way of a capacitor comprising the first input electrode143 of the first plate 140 and the second output electrode 152 of thesecond plate 150 and the capacitor comprising the second ring-shapedelectrodes 146 and 154 of the first and second plates 140 and 150. Inthe comparison circuit 350, these signals 40-s and 41-s aredifferentially amplified and transmitted as the signal 55-s shown in (q)of FIG. 17 to the phase detecting circuit 360. Thus, the output terminal304 of the rotational angle signal output circuit 380 goes to "0" andthe output terminal 303 of the reference angular position signal outputcircuit 370 remains "0".

As having been described hereinabove, when the second plate 150 isrotated by the rotation of the shaft 120 so that the first and secondreference angular position detection electrodes 141 and 142 and thefirst and second rotational position detection electrodes 143 and 144which are arranged on the first plate 140 and the first and secondoutput electrodes 151 and 152 of the second plate 150 are successivelyopposed to each other, signals are generated which go to "1" and "0"repeatedly as shown in (t) and (u) of FIG. 17. In (t) of FIG. 17 isshown the output signal at the output terminal 303 of the referenceangular position signal output circuit 370 and shown in (u) of FIG. 17is the output signal at the output terminal 304 of the rotationalposition signal output circuit 380. With the waveforms of these outputsignals, an interval a indicates that the first output electrode 151 ofthe second plate 150 is positioned opposite to the first input referenceangular position detection electrode 141 of the first plate 140 and itindicates the reference angular position which appears once for everyrotation of the shaft 120. Intervals b and c respectively indicate thatthe first output electrode 151 of the second plate 150 is positionedopposite to the first and second rotational position detectionelectrodes 143 and 144, respectively, of the first plate 140 and theseintervals occur alternately except where the inteval a occurs.

While, in the third embodiment described above, the first and secondreference angular position electrodes 141 and 142 of the first plate 140and the first and second output electrodes 151 and 152 of the secondplate 150 adapted to face the former electrodes are arranged as shown inFIGS. 14a and 14b, as mentioned in the description of the embodiment,this arrangement only needs to be such that the reference angularposition detection electrodes of the first plate 140 and the outputelectrodes of the second plate 150 face wholly only once for everyrotation of the shaft 120 and one electrode piece at the most facesduring the remainder of the rotation. In other words, it should beapparent from the foregoing description that the similar effect can beobtained even in extreme cases where the first plate-reference angularposition detection electrodes comprise only a pair comprising one of theelectrode pieces of 141 and the adjacent one of those of 142 and thesecond plate-output electrodes comprise only a pair comprising one ofthe electrode pieces of 151 and the adjacent one of those of 152.

The fourth embodiment of the invention will now be described withreference to the accompanying drawings.

FIG. 18 is a longitudinal sectional view showing the mechanicalconstruction of a capacity type rotation detecting apparatus accordingto the fourth embodiment of the invention in the like manner as FIG. 1bfor the first embodiment and FIG. 13 for the third embodiment. However,this embodiment differs from the first and third embodiments in that thesignal lines 141-a, 142-a, 143-a, 144-a and 145-a from the detectingcircuit section 101 provided on the printed board 130 attached to thehousing 100 are respectively connected to the associated electrodes ofthe first (fixed) plate 140. More specifically, in FIG. 19a illustratinga front view showing the surface 140a of the first plate 140 which facesthe second (rotatable) plate 150, the signal lines 141-a, 142-a, 143-a,144-a and 145-a are respectively connected via the connecting points 40,50, 60, 70 and 25 to the first and second input reference angularposition detection electrodes 141 and 142 and first and second inputrotational position detection electrodes 143 and 144, each including aplurality of pectinated electrode pieces, and the ring-shaped electrode145 of the first plate 140. The first and second input reference angularposition detection electrodes 141 and 142 have their electrode piecesarranged at respective different intervals and respectivelyinterconnected on the back surface by way of the connecting points 40and 50. The first and second input rotational position detectionelectrodes 143 and 144 have their electrode pieces radially arrangedalternately in those portions where the first and second input referenceangular position detection electrodes 141 and 142 are not present andrespectively interconnected on the front surface as well as on the backsurface by way of the connecting points 60 and 70. FIG. 19b is a frontview showing the surface 150a of the second plate 150 which faces thefirst plate 140 and the output electrode 151 has its electrode piecesinterconnected electrically on the front surface and also to thering-shaped electrode 153 by a lead wire 152. It is arranged so thatwhen the second plate 150 is rotated, the output electrode 151 faceswholly the first and second input reference angular position detectionelectrodes 141 and 142, respectively, only at one position. Thering-shaped electrode 153 is arranged at a position to be opposite tothe ring-shaped electrode 145 of the first plate 140.

FIG. 20 is a circuit diagram of the detecting circuit section 101 inFIG. 18. In the Figure, a terminal 301 is a power supply terminal towhich is applied a constant voltage +V_(C). A terminal 302 is a groundterminal. Numeral 310 designates a known type of CR oscillator circuit,320 a first reference signal generating circuit, 330 a second referencesignal generating circuit, 340 a capacitor group comprising theelectrodes 151 and 153 of the second plate 150 and the electrodes 141,142, 143, 144 and 145 of the first plate 140, 350 a comparison circuit,360 a phase detecting circuit, 370 a reference angular position signaloutput circuit, 380 a rotational position signal output circuit, 303 areference angular position signal output terminal, and 304 a rotationalposition signal output terminal.

The CR oscillator circuit 310 and the first reference signal generatingcircuit 320 form a first periodic signal supply circuit, and the CRoscillator circuit 310 and the second reference signal generatingcircuit 330 form a second periodic signal supply circuit. Also, thecomparison circuit 350, the phase detecting circuit 360, the referenceangular position signal output circuit 370 and the rotational positionsignal output circuit 380 form a detecting circuit.

Next, the operation of the above-described construction will bedescribed with reference to FIGS. 20, 21a to 21d and 22. In FIG. 20, theoscillation waveform 10-s shown in (a) of FIG. 22 is produced by the CRoscillator circuit 310 comprising inverter gates 311 and 312, resistors313 and 314 and a capacitor 315. This oscillation waveform 10-s is thentransmitted to the first reference signal generating circuit 320, andthe waveform 11-s in (c) of FIG. 22 obtained by the 2:1 frequencydivision of the oscillation waveform 10-s and the waveform 21-s shown in(d) of FIG. 22, which is opposite in phase to the waveform 11-s, areproduced through a D-type flip-flop 321 and inverter gates 322, 323 and324. The waveform 10-s is also transmitted to the second referencesignal generating circuit 330, and a signal of the same phase as theoscillation waveform 10-s and the signal 20-s of the opposite phaseshown in (b) of FIG. 22 are produced.

Description will be first made of the case where the shaft 120 isrotated so that the second plate 150 is rotated bringing its outputelectrode 151 in a position opposite to the first input referenceangular position detection electrode 141 of the first plate 140 as shownin FIG. 21a.

In this case, the whole of the output electrode 151 of the second plate150 is opposite to the first input reference angular position detectionelectrode 141 of the first plate 140. The signal 11-s obtained by the2:1 frequency division of the oscillation waveform 10-s is appliedthrough the signal line 141-a to the first input reference angularposition detection electrode 141 of the first plate 140 so that a signalof the same phase as the signal 11-s is generated on the lead wire 152shown in FIG. 14b by way of a capacitor (341 in FIG. 20) comprising thefirst input reference angular position detection electrode 141 of thefirst plate 140 and the output electrode 151 of the second plate 150,and the signal is then transmitted as the signal 30-s in (e) of FIG. 22to a signal line 30-l leading to the comparison circuit 350 of FIG. 20via the connecting point 25 by a capacitor (345 in FIG. 20) comprisingthe ring-shaped electrode 153 of the second plate 150 and thering-shaped electrode 145 of the first plate 140. Note that the waveformof the signal 30-s is biased by a voltage Va determined by resistors 352and 353 of the comparison circuit 350. The signal 30-s is amplified byan amplifier circuit comprising an operational amplifier 356(hereinafter simply referred to as an OP AMP) and a resistor 355 of thecomparison circuit 350, reshaped by inverter gates 357 and 358 anddelivered onto a signal line 50-l in FIG. 20 as a signal 50-s of thewaveform shown in (g) of FIG. 22 and delayed by ΔT from the signal 11-s.Here, the delay ΔT represents the capacitor response delay time and theswitching delay time of the OP AMP 356.

The signal 50-s is then transmitted to the phase detecting circuit 360and is applied to the data terminal of its D-type flip-flops 363, 364,365 and 366, respectively. Also, the signal 70s shown in (i) of FIG. 22is applied to the clock terminal of the D-type flip-flop 363 and asignal of the phase opposite to the signal 70-s is applied to the clockterminal of the D-type flip-flop 364. Also, the signal 80-s shown in (j)of FIG. 22 is applied to the clock terminal of the D-type flip-flop 365and a signal of the phase opposite to the signal 80-s is applied to theclock terminal of the D-type flip-flop 366. When the above-mentionedsignal 50-s is applied to the data terminal of the D-type flip-flops363, 364, 365 and 366, respectively, a "1" is generated at the outputterminal Q of the D-type flip-flops 363 and 364, respectively, and a "0"is generated at the output terminal Q of the D-type flip-flops 365 and366, respectively. The output signals of the D-type flip-flops 363, 364,365 and 366 are transmitted to the reference angular position signaloutput circuit 370 so that a "0" is generated at the output terminal ofa NAND gate 371, a "1" at the output terminal of a NAND gate 372 and a"1" at the output terminal of a NAND gate 373, and a switching circuitcomprising resistors 375 and 377 and a transistor 376 generates at theoutput terminal 303 a signal "0" indicating that the output electrode151 of the second plate 150 is opposite to the first input referenceangular position detection electrode 141 of the first plate 140. In thiscase, the output terminal 304 of the rotational position signal outputcircuit 380 is at "0".

Next, description will be made of the case where the shaft 120 shown inFIG. 18 is rotated so that the second plate 150 is rotated bringing itsoutput electrode 151 in a position opposite to the second inputreference angular position detection electrode 142 of the first plate140 as shown in FIG. 21b. In this case, the whole of the outputelectrode 151 of the second plate 150 is positioned opposite to thesecond input reference angular position detection electrode 142 of thefirst plate 140. A signal 21-s of the phase opposite to the signal 11-sis applied via the signal line 142-a to the second input referenceangular position detection electrode 142 of the first plate 140 so thatthe signal 21-s is transmitted by way of a capacitor (342 in FIG. 20)comprising the electrode pieces of the second input reference angularposition detection electrode 142 and the electrode piees of the outputelectrode 151 of the second plate 150 and then, as mentioned previously,transmitted as a signal 31-s (see (e) of FIG. 22) to the signal line30-l leading to the comparison circuit 350. The signal 31-s is amplifiedby the OP AMP 356 and a signal 51-s (see (g) of FIG. 22) is generated onthe signal line 50-l in FIG. 20. Thus, in the like manner as describedpreviously, a "0" is generated at the output terminal Q of the D-typeflip-flops 363 and 364, respectively, and a "1" is generated at theoutput terminal Q of the D-type flip-flops 365 and 366, respectively. Asa result, the output terminal of the NAND gate 371 goes to "1" and theoutput terminal of the NAND gate 372 goes to "0", so that the outputterminal of the NAND gate 373 goes to "0" and a signal "1" is generatedat the output terminal 303 indicating that the output electrode 151 ofthe second plate 150 is opposite to the second input reference angularposition detection electrode 142 of the first plate 140. In this case,the output terminal 304 of the rotational position signal output circuit380 remains "0".

Next, description will be made of the case where the output electrode151 of the second plate 150 is positioned opposite to the first inputrotational position detection electrode 143 of the first plate 140 asshown in FIG. 21c. A signal of the same phase as the oscillationwaveform 10-s is applied to the first input rotational positiondetection electrode 143 of the first plate 140 so that the signal 40-sshown in (f) of FIG. 22 is generated on the signal line 30-l by way of acapacitor (343 in FIG. 20) comprising the output electrode 151 of thesecond plate 150 and the first input rotational position detectionelectrode 143 of the first plate 140 and the capacitor (345 in FIG. 20)comprising the ring-shaped electrode 153 of the second plate 150 and thering-shaped electrode 145 of the first plate 140. This signal 40-s istransmitted to the comparison circuit 350 and thus the signal 60-s shownin (h) of FIG. 22 is generated on the signal line 50-l. The signal 60-sis transmitted to the phase detecting circuit 360 so that a "1" isgenerated at the output terminal Q of the D-type flip-flop 363 and a "0"is generated at the output terminal Q of the D-type flip-flop 364.Consequently, a "1" is generated at the output terminal of the NAND gate381 of the rotational angle signal output circuit 380 and a "0" isgenerated at the output terminal of the NAND gate 382, thus generating asignal "1" at the output terminal 304 of the rotational angle signaloutput circuit 380 indicating that the output electrode 151 of thesecond plate 150 is opposite to the first input rotational positiondetection electrode 143 of the first plate 140. In this case, a "0" isgenerated at the output terminal 303.

When the output electrode 151 of the second plate 150 is positionedopposite to the first input rotational position detection electrode 143of the first plate 140, depending on the position of the shaft 120,there are cases where some of the electrodes pieces of the outputelectrode 151 may face the first input reference angular positiondetection electrode 141 of the first plate 141. However, the number ofsuch an electrode piece will be only one at the most and can be ignored.

Next, when the output electrode 151 of the second plate 150 ispositioned opposite to the second input rotational position, detectionelectrode 144 of the first plate 140 as shown in FIG. 21d, a signal 41-s(see (f) of FIG. 22) is generated on the signal line 30-l in FIG. 20 sothat a signal 61-s (see (h) of FIG. 22) is generated on the signal line50-l, and a signal "0" is generated at the output terminal 304 of therotational position signal output circuit 380 in the same manner, asmentioned previously, indicating that the output electrode 151 of thesecond plate 150 is opposite to the second input rotational positiondetection electrode 144 of the first plate 140. In this case, a "0" isgenerated at the output terminal 303.

While, when the output electrode 151 of the second plate 150 ispositioned opposite to the second input reference angular positionelectrode 144 of the first plate 140, depending on the rotationalposition of the shaft 120, one piece at the most of the electrode piecesof the output electrode 151 will face the second input reference angularposition detection electrode 142, this can be ignored for the reason asmentioned previously.

As described hereinabove, when the second plate 150 is rotated by therotation of the shaft 120 so that the first and second reference angularposition detection electrodes 141 and 142 and the first and secondrotational position detection electrodes 143 and 144, which are arrangedon the first plate 140, successively face the output electrode 151 ofthe second plate 150, signals are generated as shown in (a) and (b) ofFIG. 23, and, in (b) of FIG. 23 the interval, a is a time during whichthe output electrode 151 of the second plate 150 is positioned oppositeto the second input reference angular position detection electrode 142of the first plate 140 and the interval a appears once for everyrotation of the shaft 120. The intervals b and c respectively indicatetimes during which the output electrode 151 of the second plate 150 ispositioned opposite to the first input rotational position detectionelectrode 143 and the second input rotational position detectionelectrode 144, respectively, of the first plate 140.

While, in the above-described fourth embodiment, the first and secondinput reference angular position detection electrodes 141 and 142 of thefirst plate 140 and the output electrode 151 of the second plate 150,which is adapted to face the former electrodes, are arranged as shown inFIGS. 19a and 19b, as also mentioned in the description of theembodiment, the arrangement needs only to be such that the referenceangular position detection electrodes of the first plate 140 and theoutput electrode of the second plate 150 face each other wholly once forevery rotation of the shaft 120 and only one electrode piece thereof atthe most is allowed to face during the remainder of the rotation. Inother words, the similar effect as mentioned previously can be obtainedeven in such an extreme case where the first plate-reference angularposition detection electrodes comprise only a pair comprising one of theelectrode pieces of 141 and the adjacent one of those of 142 and thesecond plate-output electrode comprises only a single electrode piece.

From the foregoing description it will be seen that the capacity typerotation detecting apparatus according to this invention has a greatadvantage that the rotational position and reference angular position ofa rotational object under measurement can be accurately detectedsimultaneously by one and the same apparatus irrespective of therotational speed of the rotational object under measurement.

We claim:
 1. A capacitor type rotation detection apparatus comprising:afirst plate having a plurality of electrode pieces of a first inputelectrode and a plurality of electrode pieces of a second inputelectrode arranged along a circumference at respective equally givenintervals and contiguously intermeshed, said first input electrodepieces forming a first input reference angular position detectionelectrode comprising a set of said first input electrode pieces selectedat respective different intervals and further forming a first inputrotational position detection electrode comprising a set of said firstinput electrode pieces other than said first input reference angularposition detection electrode pieces, and said second input electrodepieces forming a second input reference angular position detectionelectrode comprising a set of said second input electrode pieces eachthereof being positioned adjacent to one of said first input referenceangular position detection electrode pieces on one side thereof andfurther forming a second input rotational position detection electrodecomprising a set of said second input electrode pieces other than saidsecond input reference angular position detection electrode pieces, andan input ring-shaped electrode; a second plate having an outputelectrode arranged to face said first and second input reference angularposition detection electrodes and an output ring-shaped electrodeconnected to said output electrode and arranged to face said inputring-shaped electrode; a first periodic signal supply circuit forsupplying two periodic signals of opposite phase to said first andsecond input reference angular position detection electrodes,respectively, at a predetermined period; a second periodic signal supplycircuit for supplying two periodic signals of opposite phase and havinga period different from the period of said periodic signals supplied tosaid first and second input reference angular position detectionelectrodes to said first and second input rotational position detectionelectrodes; and a detecting circuit for detecting a rotational positionand a reference angular position of said second plate in accordance withperiodic signals appearing at said output electrode.
 2. An apparatusaccording to claim 1, wherein said first periodic signal supply circuitincludes a frequency divider circuit for dividing the frequency of theperiodic signals from said second periodic signal supply circuit.
 3. Anapparatus according to claim 2, wherein said detecting circuit comprisesa phase detecting circuit for detecting the phase relation betweenperiodic signals of the same period as the periodic signal supplied tosaid first or second input reference angular position detectionelectrode and a periodic signal appearing at said output electrode togenerate an output signal, a reference angular position signal outputcircuit responsive to the output signal from said phase detectingcircuit to generate a reference angular position signal, and arotational position signal output circuit responsive to the outputsignal from said phase detecting circuit to generate a rotationalposition signal.
 4. An apparatus according to claim 1 wherein saiddetecting circuit comprises a phase detecting circuit for detecting thephase relation between periodic signals of the same period as theperiodic signal supplied to said first or second input reference angularposition detection electrode and a periodic signal appearing at saidoutput electrode to generate an output signal, a reference angularposition signal output circuit responsive to the output signal from saidphase detecting circuit to generate a reference angular position signal,and a rotational position signal output circuit responsive to the outputsignal from said phase detecting circuit to generate a rotationalposition signal.
 5. A capacity type rotation detecting apparatuscomprising:a first plate having a plurality of electrode pieces of afirst input electrode and a plurality of electrode pieces of a secondinput electrode arranged along a circumference at respective equallygiven intervals and contiguously intermeshed, said first input electrodepieces forming a first input reference angular position detectionelectrode comprising a set of said first input electrode pieces selectedat respective different intervals and further forming a first inputrotational position detection electrode comprising a set of said firstinput electrode pieces other than said first input reference angularposition detection electrode pieces, and said second input electrodepieces forming a second input reference angular position detectionelectrode comprising a set of said second input electrode pieces eachthereof being positioned adjacent to one of said first input referenceangular position detection electrode pieces on one side thereof andfurther forming a second input rotational position detection electrodecomprising a set of said second input electrode pieces other than saidsecond input reference angular position detection electrode pieces, anda first and a second input ring-shaped electrode; a second plate havinga first and a second output electrode arranged to face said first andsecond input reference angular position detection electrodes,respectively, and a first and a second output ring-shaped electrodeconnected to said first and second output electrodes, respectively, andarranged to face said first and second input ring-shaped electrodes,respectively; a first periodic signal supply circuit for supplying twoperiodic signals of opposite phase at a predetermined period to saidfirst and second input reference angular position detection electrodes,respectively; a second periodic signal supply circuit for supplying twoperiodic signals of opposite phase and having a period different fromthe period of said periodic signals supplied to said first and secondinput reference angular position detection electrodes to said first andsecond input rotational position detection electrodes, respectively; anda detecting circuit for detecting a rotational position and a referenceangular position of said second plate in accordance with periodicsignals appearing at said first and second output electrodes when saidsecond plate is rotated relative to said first plate.
 6. An apparatusaccording to claim 5, wherein said first periodic signal supply circuitincludes a frequency divider circuit for dividing the frequency of theperiodic signals from said second periodic signal supply circuit.
 7. Anapparatus according to claim 6, wherein said detecting circuit comprisesa comparison circuit for differentially amplifying periodic signalsappearing at said first and second output electrodes on said secondplate to generate an output signal, a phase detecting circuit fordetecting the phase relation between the output signal from saidcomparison circuit and the periodic signal supplied to said first orsecond input reference angular position detection electrode to generatean output signal, a reference angular position signal output circuitresponsive to the output signal from said phase detecting circuit togenerate a reference angular position signal, and a rotational anglesignal output circuit responsive to the output signal from said phasedetecting circuit to generate a rotational angle signal.
 8. An apparatusaccording to claim 5 wherein said detecting circuit comprises acomparison circuit for differentially amplifying periodic signalsappearing at said first and second output electrodes on said secondplate to generate an output signal, a phase detecting circuit fordetecting the phase relation between the output signal from saidcomparison circuit and the periodic signal supplied to said first orsecond input reference angular position detection electrode to generatean output signal, a reference angular position signal output circuitresponsive to the output signal from said phase detecting circuit togenerate a reference angular position signal, and a rotational positionsignal output circuit responsive to the output signal from said phasedetecting circuit to generate a rotational position signal.